Replace reads in squashfs with positional reads

In most cases, we know exactely where the data that we want to read is
on disk, so instead of using read() on the squashfs (or lseek + read),
the code can in many places be cleaned up to use the pread wrapper
read_data_at instead.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 5 insertions, 14 deletions

diff --git a/lib/sqfs/frag_reader.c b/lib/sqfs/frag_reader.c
index 87e4c35..721286c 100644
--- a/lib/sqfs/frag_reader.c
+++ b/lib/sqfs/frag_reader.c
@@ -31,11 +31,6 @@ static int precache_block(frag_reader_t *f, size_t i)
 	if (i == f->current_index)
 		return 0;
 
-	if (lseek(f->fd, f->tbl[i].start_offset, SEEK_SET) == (off_t)-1) {
-		perror("seeking to fragment location");
-		return -1;
-	}
-
 	compressed = (f->tbl[i].size & (1 << 24)) == 0;
 	size = f->tbl[i].size & ((1 << 24) - 1);
 
@@ -44,8 +39,10 @@ static int precache_block(frag_reader_t *f, size_t i)
 		return -1;
 	}
 
-	if (read_data("reading fragment", f->fd, f->buffer, size))
+	if (read_data_at("reading fragment", f->tbl[i].start_offset,
+			 f->fd, f->buffer, size)) {
 		return -1;
+	}
 
 	if (compressed) {
 		ret = f->cmp->do_block(f->cmp, f->buffer, size,
@@ -95,11 +92,8 @@ frag_reader_t *frag_reader_create(sqfs_super_t *super, int fd,
 		goto fail_rd;
 
 	/* read the meta block offset table */
-	if (lseek(fd, super->fragment_table_start, SEEK_SET) == (off_t)-1)
-		goto fail_seek;
-
-	if (read_data("reading fragment table", fd, locations,
-		      blockcount * sizeof(locations[0]))) {
+	if (read_data_at("reading fragment table", super->fragment_table_start,
+			 fd, locations, blockcount * sizeof(locations[0]))) {
 		goto fail;
 	}
 
@@ -139,9 +133,6 @@ frag_reader_t *frag_reader_create(sqfs_super_t *super, int fd,
 	f->block_size = super->block_size;
 	f->current_index = count;
 	return f;
-fail_seek:
-	perror("seek to fragment table");
-	goto fail;
 fail_rd:
 	perror("reading fragment table");
 	goto fail;